Metal recovery apparatus



1952 N. B. AUKERMAN METAL RECOVERY APPARATUS Filed April 17', 1948 INVENTOR NATHAN/EL B. AUKERMAN ATTORNEY Iatentecl Nov. 25, 1952 METAL RECOVERY APPARATUS Nathaniel B. Aukerman, Wilmington, DeL; Sara A. Ingram, executrix of said Nathaniel B.

Aukerman, deceased Application April 17, 1948, Serial No. 21,610

6 Claims.

This invention relates to apparatus for recovering noble metals from solution and especially for recovering silver from photographic processing baths, and is more particularly directed to improved, self-contained units of the immersed electrocouple type in which a zinc plate is enveloped in a porous sheath and the sheath is partially covered externally with a strip winding of copper or other electropositive metal.

Immersed electrocouple-type units for recovering silver from photographic processing solutions have been widely used commercially, and have been described, for instance, in my prior U. S. Patents 1,425,935 and 2,292,314. The technological advances in photographic processing procedure, particularly in the chemical composition of the solutions and the design of the equipment, have given rise to certain difiiculties in the use of the recovery units heretofore available. Thus, while such units performed satisfactorily in the older fixing baths containing only acetic acid, their use in the newer rapid fixing baths containing also ammonium chloride and boric acid was accompanied by the formation of a turbidity in the solutions and by deposition of silver in the sludge at the bottom of the fixing tank where its recovery was very diflicult.

Additionally, the bulk of the prior art units, particularly their thickness, precluded their use in many places, such as in mechanical processing :iw

plants and in the developing of motion picture film, where there is very little extra space between mechanism and tank. walls. The problem was not merely one of redesigning the former units to make them thinner and less bulky;v it was imperative that the unit with decreased bulk also provide a silver deposit which was adherent and which formed quantitatively in the desired location on the unit. It was, moreover, necessary that the unit provide such performance in any of the photographic processing solutions in common use at the present time.

Now according to the present invention I have found that an improved, self-contained metal recovery unit of the immersed electrocouple type which is thin enough to be used in close-clearance equipment and which nevertheless provides a quantitative deposit of recovered metal on the unit even in rapid fix baths may comprise a zinc plate enveloped in a porous sheath, said sheath 7 being partially covered externally with a strip winding of an electropositive metal. The apparatus preferably may also include a frame of nonconducting material, such as wood, around the outer edges of the sheath, the ends of the frame 2 being narrower than the sides. In a particularly preferred embodiment of the apparatus there may also be included at least a partial covering of iron around the zinc plate within the porous sheath and electrically connected to the strip winding of electropositive metal.

In Figures 1a, lb, and 1c of the drawings there are illustrated three successive stages in the preparation of a preferred metal recovery unit of this invention, in which a zinc plate is covered by two iron plates and the whole is enclosed in a porous sheath and Wound externally with an electropositive metal. Figure 1ashows a zinc plate I about to be covered, bottom and top, with iron plates l2 and I3. Clipped to the plate l3 so as to make electrical contact therewith is a copper strip, Id. In Figure 1b, the assembly of Figure 1a. is shown inverted on a porous sheath material i, with sealing flaps 5 protruding. In Figure 1c, the sheath has been wrapped around the assembly of Figure 1a and sealed up, with the ends of copper strip M protruding out through the sheath. A spiral winding 2 of electropositive metal such as copper has been wrapped around the outside of the sheath, making contact with the ends of strip Hi.

In the aspect of the invention the iron plates may be about the same size as the zinc plate and are in contact with the zinc in such a manner as to give the maximum zinc-to-iron contact. Either or both of the iron plates are electrically connected to the external winding of electropositive metal. A single iron plate may be used instead of the pair of plates shown.

In Figure 2 of the drawings, there is illustrated an embodiment of the invention in which a zinc plate is enclosed in a porous envelope or sheath l. The sheathed plate is partially covered externally with a strip winding of an electropositive metal, in this case a spiral winding of copper ribbon 2 being used. The electrocouple thus produced is held in a frame of non-conducting material, such as wood, comprising sides 3 and ends c, the width of the sides being greater than that of the ends so as to provide room for the solution in which the unit is immersed to circulate over both sides of the electrocouple. The ends of the electrocouple are held in grooves in the frame ends 4. The closure of the porous sheath is accomplished by sealed flaps 5, an insoluble paste being used for sealing. A cord 3 is provided as a means of suspending the unit in a solution containing a dissolved noble metal such as silver. The entire unit may, if desired, be enclosed in netting (not shown), such as cotton mosquito netting, to

insure that deposited silver will not escape from the unit even if dislodged by rough handling.

Another preferred embodiment using the internal iron covering in the form of a spiral winding is illustrated in Figure 3, in which a zinc plate 7 is enclosed in a paper sheath I, which is sealed by flap 5. The sheathed plate is partially covered externally with a spiral winding of copper ribbon 2. In Figure 3 the paper sheath is cut away along line 8-8 to reveal the covering of iron 9, in this case a strip winding in direct contact with the zinc plate. This winding 9, continues toward the left of and below the cutaway line 88, coming out of the sheath through close-fitting slot l and making electrical connection H, with the copper ribbon winding 2.

The zinc plate which serves as the core of the unit may be any desired length and shape. I have found, for instance, that a plate inch thick, about 2 inches wide, and 8 to 10 inches long gives very satisfactory results, providing an amount of zinc which is chemically equivalent to somewhat more silver than such a unit is ordinarily called upon to deposit. Thus, there is no deficiency of zinc during operation, yet after use, the unit does not contain a large excess of zinc to be wasted. Units of thirty inches or more in length have been found to operate satisfactorily. The quantity and length of units should, of course, be selected with a View to the quantity of silver or other noble metal in the bath being worked, the rate at which recovery is to be effected, and the space available in the solution tank.

The porous sheath or envelope in which the zinc plate is enclosed may consist of one or more layers of a porous material such a paper, but should be so constructed that the zinc is completely enclosed and access to it by the solution can come about principally by penetration through the porous material. The porosity of the sheath should be about equal to that of 30-point kraft paper. A variety of papers, such as sulfite, rag, and parchmentized papers, or material of equal porosity, may be used, but I have obtained particularly good results using a single or double layer of 30-point kraft paper.

A paper sheath may be made by wrapping the paper around the zinc, turning down the ends, and sealing all edges with an adhesive which becomes insoluble upon drying, such as casein glue or other marine glues. In order to obtain maximum tightness of the sheath, I may saturate the paper with water before using it for wrapping the zinc.

The partial covering of electropositive metal. may be applied to the sheathed zinc plate by wrapping a strip or strips of the metal around the outside of the sheath. Direct connection between the zinc and the electropositive metal is not necessary. The electropositive metal may be one standing below zinc in the electromotive force series of metals, and advantageously may, for example, be copper, lead, or silver. It may be in the form of wire, or it may be relatively wide and thick. It is particularly preferred that the electropositive metal be in the form of ribbon, that is, of relatively small width and thickness in proportion to its length.

The copper or other metal strip may be only long enough to go once around the outside of the sheath, and a series of such disconnected bands may be used. Alternatively, it may be in the form of a screen or grid around the sheath. However, maximum ease of manufacture is attained by using copper ribbon and applying it as a continuous, firmly wound spiral as illustrated in the drawings. This provides a further advantage in that when the unit has been used to the limit of its capacity and has acquired a heavy coating of silver, the copper ribbon may be stripped out in a single, continuous piece, thus simplifying refinement of the silver. The copper ribbon is unaffected by the silver-recovery process and may be reused in a new unit. The spiral winding also acts to hold the porous sheath tightly around the zinc and protects it against tearing or puncture by external objects.

The area covered by the copper or other electropositive metal need be only a part of the total area of ensheathed zinc. Advantageously the proportion should be less than half, and in a spirally wound unit the distance between adjacent windings, for instance, may be from to 2 inches when the width of theribbon used for the winding is inch.

When an iron covering is used in direct contact with the zinc plate according to a preferred embodiment of the invention such as illustrated in Fi ures 10 and 3 the iron covering preferably should be flat. The iron covering may be in the form of wire or ribbon and it may be wound spirally around the zinc plate as shown in Figure 3 or it may consist of an iron screen or grid, or a plate or p ates as already mentioned in connection with Figure 1c. In any case it should be in electrical contact with the zinc and an electrical connection should extend through the paper sheath and make electrical contact with the external electropositive metal strip.

When reference is made to iron it will be understood to include steel and alloys which are predominantly iron, although ordinary mild or low-carbon steel is preferred.

The embodiment of the invention containing the internal iron covering may, if desired, be enclosed in a frame such as illustrated in Figure 2.

The frame shown in Figure 2 is optional, and may be omitted, particularly in units which are to be used in mechanical fixing tanks havhis close clearances. The frame is of value, however. in providing additional protection against humpim of the unit. It may be made of phenolformaldehyde or other plastic resin, but wood is about ecually satisfactory and is preferred because of its lower cost.

The improved units of the present invention are used in the same manner as prior art units, in that they are merely immersed in the solution from which silver or other noble metal is to be recovered. The silver collects on the unit quantitatively, that is, all of the silver that is released by the action of the unit is retained on the unit and there is no turbidity formed in the solution and no loss of silver in tank sludges. The units may be used in the working photographic developing bath or in a spent bath which is ready for discard, and if desired, the units may be used in a hath not heavily loaded with silver. The silver formed on the unit is adherent, coherent, and of very high purity. Furthermore, by having the silver removed in this manner, the bath is rejuvenated to the extent that the ordinary volume of film being processed is approximately doubled, thus effecting a saving of chemicals. time, and labor.

I claim:

1. Apparatus of the self-contained, immersed electro-couple type for recovering noble metals from solution comprising a zinc plate partially covered with an iron covering, a paper sheath enveloping said iron-covered plate, a strip winding of an electropositive metal partially covering, externally, said paper sheath, and an electrical connection between said iron covering and said electropositive metal winding.

2. Apparatus of the self-contained, immersed electro-couple type for recovering noble metals from solution comprising a zinc plate enveloped in a paper sheath, the sheath being spirally Wound externally with copper ribbon.

3. Apparatus adapted to be immersed in aqueous silver solutions and to deposit silver therefrom by electrolytic action, said apparatus comprising a zinc plate completely enclosed. in a tight-fitting envelope of 30-point kraft paper, and a copper ribbon spirally wound around the outside of said envelope.

4. Apparatus adapted to be immersed in aqueous silver solutions and to deposit silver therefrom by electrolytic action, said apparatus comprising a zinc plate wound with iron ribbon making electrical contact therewith, the winding only partially covering the surface of the zinc, a tightfitting envelope of 30-point kraft paper enclosing said iron ribbon-wound plate, and a copper ribbon spirally wound around the outside of said envelope and electrically connected to said iron 31 ribbon.

5. Apparatus adapted to be immersed in aqueous silver solutions and to deposit silver therefrom by electrolytic action, said apparatus comprising a zinc plate partially covered with an iron plate making electrical contact therewith, a tight-fitting envelope of 30-point krait paper enclosing said zinc plate and iron covering, and a copper ribbon spirally wound around the outside of said envelope and electrically connected to said iron plate.

6. Apparatus of the self-contained, immersed electro-couple type for recovering noble metals from solution comprising a zinc plate enveloped in a paper sheath, the sheath being spirally Wound externally with copper ribbon, and a nonconducting frame enclosing the outer edges of said enveloped and spirally wound plate.

NATHANIEL B. AUKERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 577,134 Harrison Feb. 16, 1897 2,292,314 Aukerman Aug. 4, 1942 FOREIGN PATENTS Number Country Date 451,703 Great Britain Aug. 11, 1936 452,466 Great Britain Aug. 24, 1936 928,031 France May 19, 1947 OTHER REFERENCES Corrosion Resistance of Metals and Alloys, page 33, McKay, 1936, Reinhold Publishing Corp., New York, N. Y. 

1. APPARATUS OF THE SELF-CONTAINED, IMMERSED ELECTRO-COUPLE TYPE FOR RECOVERING NOBLE METALS FROM SOLUTION COMPRISING A ZINC PLATE PARTIALLY COVERED WITH AN IRON COVERING, A PAPER SHEATH ENVELOPING SAID IRON-COVERED PLATE, A STRIP WINDING OF AN ELECTROPOSITIVE METAL PARTIALLY COVERING, EXTERNALLY, SAID PAPER SHEATH, AND AN ELECTRICAL CONNECTION BETWEEN SAID IRON COVERING AND SAID ELECTROPOSITIVE METAL WINDING. 